Our version of this rustic British classic transforms it into a quick, easy main for any night of the week. For an all-in-one meal in single servings, you can divide the filling among four 9-ounce ramekins before topping it with the mashed potatoes. Bake on a baking sheet until the filling is bubbly around the edges and the potatoes are lightly browned, about 15 minutes.
If using a glass baking dish, instead of broiling at the end, increase the oven temperature to 450ºF and bake until the cheese is bubbling and golden.
Preheat the oven to 425ºF. Heat the oil in a medium ovenproof skillet over medium-high heat. Add the garlic, carrots and onions; cook until tender and beginning to brown, about 5 minutes. Add the turkey and thyme, and continue to cook, breaking the turkey up with a spoon, until the turkey is cooked through and lightly browned. Stir in the ketchup and cook until lightly caramelized. Stir the broth and flour together in a small bowl until smooth, and then pour into the skillet. Cook until thickened, about 2 minutes. Stir in the peas and season with ¼ teaspoon salt.
Meanwhile, place the potatoes in a medium pot and cover with cold salted water. Bring to a boil, lower the heat and simmer until tender when pierced with a knife. Drain the potatoes and return to the pot over low heat. Stir the potatoes for a couple of minutes to dry them out. Add the milk, cheese and scallions, and mash until smooth. Season with salt and pepper.
Swirl the mashed potatoes over the filling. Lightly mist with nonstick cooking spray and bake until the potatoes are lightly browned and the turkey filling is bubbly around the edges, 10 to 15 minutes.